The invention in general relates to transducers, and more particularly, to an underwater transducer adapted for low frequency sonar use.
A sonar transducer is a device for generating sound and sensing sound in water. A sonar transducer is at heart a resonator which in the case of ceramic sonar transducers, includes an electroded ferroelectric member. The application of electrical potentials to the electrodes excites mechanical motion in the ferroelectric member used to generate sound waves in the water, and mechanical forces exerted upon the ferroelectric member by sound waves in the water is used to generate an electrical potential in the electrodes to sense the sound.
A common form of sonar transducer includes a xe2x80x9cstackxe2x80x9d of ring shaped drivers, electrically connected in parallel, clamped by means of a stress rod between a tail mass, which is relatively heavy, and a head mass, which constitutes a relatively light, water driving piston. The tail mass, ceramic stack, and head mass form a two mass resonator assembly. The arrangement desirably produces small amplitude vibrations in the tail mass and large amplitude vibrations of the head mass which acts as a water driving piston. This type of transducer is commonly referred to as a xe2x80x9cTonpilzxe2x80x9d design transducer or Tonpilz transducer. The Tonpilz transducer assembly is normally housed in an inactive watertight co-axial tube or inactive housing which serves to contain the active Tonpilz assembly and protect it from water intrusion.
Presently there is no known technique to obtain both low frequency (below on kilohertz) and higher 1-5 kHz response other than using parametric techniques which are limited by poor conversion efficiency and beam widths too narrow to be useful for wide area coverage. This is especially important in the areas of transmit transducers and arrays for anti-submarine warfare (ASW), communications and anti-mine warfare for surface, subsurface and air-launched applications as well as geophysical exploration and target simulation, for example. In the oil exploration industry, broadband coherent sources are greatly desired to take over the role of environmentally prohibitive air guns and explosive sources, for example. Greater frequency diversity provided by a single device which has both high and low frequency capability would be of significant benefit to both naval and geophysical applications.
Accordingly, a device that provides co-location of both low-frequency and high frequency or broadband signal processing is highly desired.
The present invention uses the normally inert housing of the Tonpilz projector to produce useful low frequency sound below the band of the Tonpilz element when used with flexural (flextensional) or slotted cylinder projectors as well as above the band of the Tonpilz element when used with complete cylinders.
The invention permits a relatively small Tonpilz or piston type transducer element to have a powerful and efficient (60-90%) low frequency surveillance transmit capability in addition to the normal tactical band capability normally associated with this type of element. In a preferred embodiment, a magnetostrictive, electrostrictive or piezoelectric driven Tonpilz driver mechanism is located within an active flexural structure such as a wall driven inverse flextensional or slotted cylinder projector (SCP) assembly. The wall driven flextensional or SCP projector provides the low frequency response in a weight-and-size efficient manner and the Tonpilz element makes efficient use of the empty space inside the wall driven flextensional or SCP. Another embodiment involves the use of a complete ceramic cylinder (not slotted) to make up part of the active housing and provide source level capabilities above the band of the Tonpilz element. Due to their higher frequency there placement in relation to head mass is more critical than the low frequency SCP due to diffraction effects.
The present invention is embodied in a longitudinal vibrator assembly comprising at least one piezoceramic, magnetostrictive, or electrostrictive transducer having a coaxial housing comprised of at least one wall driven flextensional, slotted or complete cylindrical flexural member vibrating in a circumferential or radial direction and excited by a solid state transduction material.
An underwater Tonpilz or piston assembly operative in a first longitudinal vibrational frequency mode and comprising an active housing operative for radiating sound at a substantially different frequency from the longitudinal vibrational frequency mode.
A transducer device comprising a Tonpilz element having a vibrating housing actuated by ceramic, magnetostrictive alloy or electrostrictive means, the housing having a flexural or circumferential or radial mode for increasing the effective bandwidth and frequency diversity of the device.